1. Field of Invention
This invention relates to particle beam systems used in the fabrication of micro-miniature devices (integrated circuits) and is particularly directed to a new and improved apparatus and writing technique for a particle beam lithography system.
2. Prior Art
Lithographic systems utilizing a controllable electron beam for the fabrication of master masks for making integrated circuits is old in the art; one such system is described at length in the U.S. Pat. No. 3,900,737 to Collier, et al. An apparatus for controlling an electron beam by a magnetic deflection system for use in the Collier, et al., system is shown in the U.S. Pat. No. 3,801,792 to Lin.
In the Collier patent, and utilizing an apparatus as described in the Lin patent, the mask medium (resist material) upon which the electron beam is to perform its writing operation, was positioned on a motor driven stage which moved continuously and in synchronism as the beam is scanned in raster fashion in a direction perpendicular to the stage motion.
FIG. 1 herein illustrates a writing operation in an electron beam apparatus similar to the writing operation taught in the Collier patent. As shown in the Figure, the arrow X represents the movement of the stage 12 and the Y arrow represents the movement of the electron beam in a raster scan fashion by a magnetic deflection system. In this prior art embodiment, there are 512 addresses in the Y direction and 16K addresses in the X direction; an address being defined as the diameter of the electron beam spot on the medium. The circles 14 in FIG. 1 represent electron beam spots on the resist 16 and to illustrate the effect of the modulation of the electron beam certain of the spots are shown blank while others are shown solid. Modulation in the Collier, et al., apparatus occurred at the rate of 10 MHz with four rows of addresses defining a 2.0 micrometer feature width and 512 addresses defining a stripe width of 128 micrometers utilizing an address of 0.5 micrometers. There is a requirement for smaller geometry and address structure electron beam generated masks. However, when the address structure is reduced, the mask making throughput is decreased proportional to the square of the address size. At this same time, the stage speed and deflection length of the beam are both reduced by the same factor as the address reduction.
Thus, if the electron beam is decreased below the 0.5 micrometer address, such as used in the Collier, et al apparatus, as for example to a 0.25 micrometer address, the mask making throughput utilizing the raster scan writing technique of Collier, et al., will be reduced by one-fourth.